Apparatus and method for monitoring super-heating of refrigerant to improve compressor efficiency and lower energy usage

ABSTRACT

Apparatus and methodologies are provided to monitor temperature from at least two locations on an evaporator in a refrigeration system. Operational characteristics of one or more of the compressor, condenser and evaporator cooling fans are adjusted based on the difference in temperature between the two locations on the evaporator. In some systems a second evaporator may be provided along with a refrigerant control valve. Cooling air flow across the second evaporator and refrigerant distribution between the plural evaporators may also be control.

FIELD OF THE INVENTION

The present subject matter relates to refrigerators. More particularly, the present subject matter relates to improved temperature monitoring arrangements that provide increased operational efficiency opportunities.

BACKGROUND OF THE INVENTION

Certain currently available refrigeration systems employ banded temperature control schemes which operated as either ON/OFF or LOW, MED, HIGH and required operational deadbands within their temperature control systems. Such systems include certain inherent inefficiencies due to start losses and reliability penalties associated with starting and stopping a sealed system. In other systems, temperature sensing only looks at exit temperature which does not give an indication of superheat which is correlated to evaporator/system efficiency.

U.S. Pat. No. 6,718,778 B2 to Lawrence entitled “Defrost Control Method and Apparatus” discloses a defrost control system that detects the variation in flow rate of refrigerant through an evaporator while the flow is regulated to achieve a desired level of superheat at the outlet of the evaporator. When the flow rate becomes unstable, defrosting of the evaporator is triggered. In one embodiment, the apparatus uses two temperature sensors to determine the difference in temperature at a spot on the evaporator and at the outlet of the evaporator to control a defrost cycle.

In view of these concerns, it would be advantageous to provide a refrigeration system that could accurately monitor the degree of evaporator superheat, so that various system component operational aspects can be compensated to maintain an improved balance of refrigerant and air flow to maximize the use of the physical heat exchanger surface area.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

The present subject matter relates to refrigeration apparatus and methodologies for monitoring super-heating of a refrigerant to improve compressor efficiency and lower energy usage in a refrigerator. In a first embodiment, a refrigerator having a controller, a compressor, a condenser, and an evaporator is provided. The refrigerator also includes a condenser fan configured to provide air flow across the condenser and an evaporator fan configured to provide air flow across the evaporator.

At least two temperature sensors are mounted on the evaporator. The controller is configured to control operating characteristics of at least one of the compressor, the condenser fan, and the evaporator fan based on the difference in temperature between the temperature sensors.

In certain embodiments, the controller is configured to modulate the speed of the compressor while in other embodiments the controller controls the speed of the evaporator fan and/or condenser fan.

In some embodiments the temperature sensors are thermistors, which, in selected embodiments may be coupled together to form one or more voltage dividers configured to provide a reduced number of voltage inputs to the controller representative of the difference in temperature between the thermistors.

In selected embodiments, the controller is configured to control operating characteristics in accordance with a proportional-integral-differential (PID) control system based on the difference in temperature between the at least two temperature sensors.

In certain other embodiments, the refrigerator may include a second evaporator, a second evaporator fan configured to provide air flow across the second evaporator, and a refrigerant control valve configured to control distribution of refrigerant between the evaporator and the second evaporator. In such embodiments, the controller is configured to control at least one of the compressor, the condenser fan, the evaporator fan, the second evaporator fan, and the refrigerant control valve based on the difference in temperature between the at least two temperature sensors.

The present subject matter also relates to a method for improving compressor efficiency and lowering energy consumption in a refrigeration system, comprising providing a refrigeration system including a compressor, a condenser, and an evaporator. The method monitors temperature from at least two locations on the evaporator and modulates one or more of the operational speed of the compressor and air flow across one or more of the condenser and evaporator based on the difference in temperature between the at least two locations on the evaporator.

In certain of the methods, the speed of the compressor is modulated while in other methods the speed of the air flow across the evaporator and/or the condenser is modulated based on the difference in temperature between the at least two locations on the evaporator.

In selected methods temperature is monitored by providing two or more thermistors on the evaporator. Under certain of these methods, a difference in temperature is obtained by coupling the thermistors together to form one or more voltage dividers.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 provides an illustration of an exemplary embodiment of a refrigerator as may be used with the present subject matter;

FIG. 2 is a schematic illustration providing an example of a refrigeration cycle as may be used with the present subject matter;

FIG. 3 is a schematic illustration providing an example of a proportional-integral-derivative (PID) controlled refrigerator in accordance with the present technology; and

FIG. 4 is a schematic representation of a thermistors voltage divider in accordance with one embodiment of the present subject matter.

Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

As noted in the Summary section, the present subject matter is directed toward refrigeration apparatus and methodologies for monitoring super-heating of a refrigerant to improve compressor efficiency and lower energy usage in a refrigerator. In accordance with certain aspects of the present subject matter two or more temperature sensing devices are provided at various positions on one or more evaporators to monitor temperature. In so doing, effective use of heat exchanger surface area for heat transfer may be maximized, thereby minimizing thermodynamic losses associated with superheat, thereby maximizing the efficiency of the evaporator resulting in the overall refrigeration cycle becoming more efficient. The net effect of this type of operation leads to an overall reduction in steady state energy consumption.

Referring now to the drawings, FIG. 1 provides a front view of a representative refrigerator 10 incorporating an exemplary embodiment of the present invention. For illustrative purposes, the present invention is described with a refrigerator 10 having a construction as shown and described further below. As used herein, a refrigerator includes appliances such as a freezer, refrigerator/freezer combination, compact, and any other style or model of a refrigerator. Accordingly, other configurations including multiple and different styled compartments could be used with refrigerator 10, it being understood that the configuration shown in FIG. 1 is by way of example only.

Refrigerator 10 includes a fresh food storage compartment 12 and a freezer storage compartment 14. Freezer compartment 14 and fresh food compartment 12 are arranged side-by-side within an outer case 16. Breaker strip 22 and mullion 24 form a front face, and extend completely around inner peripheral edges of case 16. In addition, refrigerator 10 includes shelves 28 and slide-out storage drawers 30 which normally are provided in fresh food compartment 12 to support items being stored therein.

Refrigerator 10 is controlled by a processing device or other controller, such as a microprocessor (not shown in FIG. 1), according to user preference via manipulation of a control interface 32 mounted in an upper region of fresh food storage compartment 12 and coupled to the microprocessor. A shelf 34 and wire baskets 36 are provided in freezer compartment 14. In addition, an ice maker 38 may be provided in freezer compartment 14.

A freezer door 42 and a fresh food door 44 close access openings to fresh food and freezer compartments 12, 14, respectively. Each door 42, 44 is mounted to rotate about its outer vertical edge between an open position, as shown in FIG. 1, and a closed position (not shown) closing the associated storage compartment. Freezer door 42 includes a plurality of storage shelves 46, and fresh food door 44 includes a plurality of storage shelves 48.

FIG. 2 is a schematic view of refrigerator 10 (FIG. 1) including an exemplary sealed cooling system 60. In accordance with known refrigerators, refrigerator 10 includes a machinery compartment 62 that at least partially contains components for executing a known vapor compression cycle for cooling air. The components include a compressor 64, a heat exchanger or condenser 66, an expansion device 68, and an evaporator 70 connected in series and charged with a refrigerant. Evaporator 70 is also a type of heat exchanger which transfers heat from air passing over the evaporator to a refrigerant flowing through evaporator 70 thereby causing the refrigerant to vaporize. As such, cooled air is produced and configured to refrigerate compartments 12, 14 of refrigerator 10.

From evaporator 70, vaporized refrigerant flows to compressor 64, which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the gaseous refrigerant through condenser 66 where heat exchange with ambient air takes place so as to cool the refrigerant. A fan 72 is used to pull air across condenser 66, as illustrated by arrows A, so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant and the ambient air.

Expansion device 68 further reduces the pressure of refrigerant leaving condenser 66 before being fed as a liquid to evaporator 70. Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through refrigeration compartments 12, 14. The refrigeration system depicted in FIG. 2 is provided by way of example only. It is within the scope of the present invention for other configurations of the refrigeration system to be used as well. For example, fan 74 may be repositioned so as to push air across evaporator 70, dual evaporators may be used with one or more fans, and numerous other configurations may be applied as well.

With reference to FIG. 3, there is illustrated a schematic representation of an example of a proportional-integral-derivative (PID) controlled refrigerator 300 in accordance with the present technology. Refrigerator 300, constructed in accordance with present technology, may be provided with various components including, but not limited to, controller 302, compressor 364, evaporator 370, evaporator fan 374, condenser 366, expansion valve 368, condenser fan 372, fresh food fan 376, and damper 378.

In some embodiments of the present subject matter, as illustrated herein generally in phantom, a second evaporator 380 may be provided along with a second evaporator fan 384. In such embodiments, a refrigerant distribution control valve 382 may be provided to control distribution of refrigerant between the evaporators. Those of ordinary skill in the art will appreciate that suitable coupling of the second evaporator 382, evaporator fan 394 and control valve 382 to the remaining portions of the refrigeration system including the compressor 364 and control 302 are required. As such coupling would be well within the capabilities of those of ordinary skill in the art, no further described is deemed necessary.

Operational control devices including temperature sensor 392 within freezer compartment 314 and temperature sensor 394 within fresh food compartment 312 may also be provided and configured to transmit temperature signals to a controller 302. As previously noted with reference to FIG. 1, controllers such as controller 302 may correspond to a number of different processing devices including microprocessors or other types of microcontrollers as is well understood by those of ordinary skill in the art.

In accordance with a significant aspect of one embodiment of the present subject matter, by monitoring the temperature of the evaporator, the operation of the compressor and/or other operationally variable refrigeration components may be modulated or adjusted so that, in the instance that the compressor speed is modulated, the compressor Energy Efficiency Ratio (EER) may be maximized permitting a more efficient run cycle and/or the overall system Coefficient of Performance (COP) may be improved by modulating the compressor and/or adjusting other operational components by, for example, controlling the speed of one or more of the fans.

In particular, by employing PID control to modulate the speed of compressor 364 for example over signal line 340 from controller 302, the compressor speed can be reduced, resulting in less mass flow of refrigerant to the evaporator so that the evaporator and condenser may be held at efficient core temperatures and pressures. In so doing the extremely low evaporator temperatures that are a natural side effect of cycling systems are able to be substantially eliminated thereby shrinking the size of the refrigeration cycle and minimizing cycling losses to provide a higher compressor EER and system.

As is understood by those of ordinary skill in the art, a proportional-integral-derivative (PID) control system may be generally defined using the well recognized generic formula:

${u(t)} = {K_{c}\left( {e + {\frac{1}{T_{i}}{\int_{0}^{t}{e{t}}}} + {T_{d}\frac{e}{t}}} \right)}$

where the three summed terms represent proportional, integral, and derivative terms that, together with a multiplication constant, represent the control function u(t). Such PID control systems may be implemented in numerous manners including through hardware, software, or combinations thereof.

In accordance with present technology, a control system, including controller 302, is configured to monitor a temperature difference between at least two points on evaporator 370 to provide one or more temperature signals to controller 302. This temperature difference between the points is then analyzed in controller 302 and used to vary the speed of compressor 364, vary the speed of one or more fans such as evaporator fan 374 and/or condenser fan 372 via signals over control lines 334, 338, control refrigerant flow distribution in a multiple evaporator system, or any combination thereof, to maintain a fully flooded evaporator section against varying heat loads. This differential signal may also be utilized to determine when to terminate a defrost cycle.

In a first embodiment of the present subject matter, two thermistors 396, 398 are mounted in two variable positions on evaporator 370 as illustrated in FIG. 3. The two thermistors 396, 398 may be electrically arranged in a voltage divider circuit 400 as illustrated by thermistors 496, 498 in FIG. 4. With a supply voltage applied across terminals 502 and ground terminal 504, a temperature difference voltage is provided as an analog signal on line 510 to controller 302 for feedback to a control program stored, for example, in a memory associated with controller 302. In this embodiment, the use of voltage divider 400 permits a solution that requires reduces the required number of signal inputs to only a single input to controller 302.

In accordance with a second embodiment of the present subject matter, multiple temperature sensing devices similar to temperature sensors 396, 398, 496, 498 may be placed at various locations on evaporator 370 to provide multiple independent temperature feedback signals to controller 302. In such an instance, controller 302 is configured to calculate one or more differences and use the result as feedback in the control program. As with the previous embodiment, the voltage dividers may be used to reduce the number of inputs to the controller, or may be used to increase knowledge of the location of the gas transition point.

In all embodiments of the present subject matter, the control program of controller 302 may include provision of feedback control for PID control of the compressor, system fans, and/or damper(s) positioning, but such is not a limitation of controller 302 as the controller may also provide additional control functions relating to the overall operation of the refrigeration apparatus.

Through implementation of the present subject matter, a number of technical advantages may be obtained. These include maximizing the available evaporator surface area for reduced energy consumption of a sealed system, by ensuring a flooded evaporator(s) section, providing a low cost method of monitoring an evaporator(s) for superheat; permitting the use of a single channel to an embedded controller for monitoring temperature differential; allowing for compensation of sealed system performance due to ambient factors such as air density (atmospheric pressure), and air temperature and humidity; and permitting active charge management in a multiple evaporator system. In addition, implementation of the present subject matter provides reduced energy consumption and a more consistently performing system in all ambient conditions.

An embodiment of the present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. The technical effect of the executable code is to facilitate prediction and optimization of modeled devices and systems.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A refrigerator, comprising: a controller; a compressor; a condenser; a condenser fan configured to provide air flow across said condenser; an evaporator; an evaporator fan configured to provide air flow across said evaporator; and at least two temperature sensors located on the evaporator, wherein said controller is configured to control operating characteristics of at least one of said compressor, said condenser fan, and said evaporator fan based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 2. A refrigerator as in claim 1, wherein said controller is configured to modulate the speed of the compressor based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 3. A refrigerator as in claim 1, wherein said controller is configured to adjust the speed of the evaporator fan based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 4. A refrigerator as in claim 1, wherein said controller is configured to adjust the speed of the condenser fan based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 5. A refrigerator as in claim 1, wherein said temperature sensors are thermistors.
 6. A refrigerator as in claim 5, wherein said thermistors are coupled together to form one or more voltage divider circuits configured to provide reduced number of voltage inputs to said controller representative of the difference in temperature between the thermistors.
 7. A refrigerator as in claim 1, wherein said controller is configured to control operating characteristics in accordance with a proportional-integral-differential (PID) control system based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 8. A refrigerator as in claim 1, further comprising: a second evaporator; a second evaporator fan configured to provide air flow across said second evaporator; and a refrigerant control valve configured to control distribution of refrigerant between said evaporator and said second evaporator, wherein said controller is configured to control at least one of said compressor, said condenser fan, and said evaporator fan, said second evaporator fan, and said refrigerant control valve based on the difference in temperature between said first temperature sensor and said second temperature sensor.
 9. A method for improving compressor efficiency and lowering energy consumption in a refrigeration system, comprising: providing a refrigeration system including a compressor, a condenser, and an evaporator; monitoring temperature from at least two locations on the evaporator; and modulating one or more of the operational speed of the compressor and air flow across one or more of the condenser and evaporator based on the difference in temperature between the at least two locations on the evaporator.
 10. A method as in claim 9, wherein modulating comprises modulating the speed of the compressor based on the difference in temperature between the at least two locations on the evaporator.
 11. A method as in claim 9, wherein modulating comprises modulating the speed of air flow across the evaporator based on the difference in temperature between the at least two locations on the evaporator.
 12. A method as in claim 9, wherein modulating comprises modulating the speed of air flow across the condenser based on the difference in temperature between the at least two locations on the evaporator.
 13. A method as in claim 9, wherein monitoring temperature comprises providing thermistors at two or more location on the evaporator.
 14. A method as in claim 13, wherein the difference in temperature is obtained by coupling the thermistors together to form one or more voltage dividers.
 15. A method as in claim 9, further comprising: providing a second evaporator; providing a refrigerant control valve configured to control distribution of refrigerant between the evaporator and the second evaporator; and modulating one or more of the operational speed of the compressor, air flow across one or more of the condenser, the evaporator, and the second evaporator, and refrigerant distribution between the evaporator and the second evaporator based on the difference in temperature between the at least two locations on the evaporator. 